Basics of Setup and Hold Part - 3

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Q.1 >> Find

1. Is there any setup violation in following flop network ?
2. Maximum frequency at which following flop network work fine ?

T = 100ns (10Mhz)

Tc2q = 10ns

Tpd = 50ns

Ts = 5ns

ANS >>

There is no setup time violation if

Tc2q + Tpd < T - Ts

Tc2q + Tpd = 10 + 50 = 60 ns

T - Ts = 100 - 5 = 95 ns

So 60 < 95 (TRUE)

There is no setup violation.

So to find out maximum frequency or minimum time period at which network work is.

Tc2q + Tpd = Tmin - Ts

10 +  50 =   T  -  5

  T = 50 + 10 + 5   =   65ns

Fmax  = (1000/65) Mhz =   15.38Mhz

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Q.2 >> Find

1. Is there any setup and hold violation ?
2. Maximum frequency at which it work fine ?

ANS >>

1. To check hold violation in network we take worst hold conditions like -  This network work fine for all condition if maximum clock arrival time is less than minimum data arrival time.

Data Path : D1(min) + D2(min) + Tc2q(min) + Tpd(min) 

Minimum Data Arrival Time :  3 + 3 + 8 + 6 = 20ns

Clock Path : D1(max) + D3(max) + D4(max) + Th

Maximum Data requested Time :  6 + 6 + 6 + 2 = 20ns

Slack = Data Arrival time - Data Requested Time

= 20 - 20 = 0ns

Fortunately, This meet Slack and network will work under this condition.

2. To check setup violation in network we take worst setup conditions like -  This network work fine for all condition if maximum data arrival time is less than minimum clock arrival time.

Data Path : D1(max) + D2(max) + Tc2q(max) + Tpd(max)

Maximum Data Arrival Time :  6 + 6 + 12 + 9 = 33ns

Clock Path : D1(min) + D3(min) + D4(min) + Tclk - Ts

Minimum Clock Arrival Time :  3 + 3 + 3 + 25 - 5 = 29ns

(Minimum Data requested Time)

Slack = Data requested time - Data arrival time

= 29 - 33

= -4ns

This is HUGE neg. Slack and network will not work under this condition. Now maximum frequency at which network work fine is (Tmin) from following setup timing equation.

D1(max) + D2(max) + Tc2q + Tpd(max) = D1(min) + D3(min) + D4(min) + Tmin - Ts

6 + 6 + 12 + 9 = 3 + 3 + 3 + Tmin - 5

Tmin = 33 - 4 = 29ns

Fmax = (1000/29) Mhz = 34.4Mhz

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